Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having refractive power; a second lens having refractive power; a third lens having refractive power and cemented to the second lens; a fourth lens having refractive power; a fifth lens having refractive power and cemented to the fourth lens; a sixth lens having refractive power; a seventh lens having refractive power; and an eighth lens having refractive power. The first to eighth lenses are sequentially disposed in numerical order beginning with the first lens from an object side of the optical imaging system toward an imaging plane of the optical imaging system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication No. 10-2016-0042247 filed on Apr. 6, 2016, in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND 1. Field

The following description relates to an optical imaging system mountedin a monitoring camera.

2. Description of Related Art

A small monitoring camera is commonly mounted in a vehicle to image afront visual field and a rear visual field of the vehicle. For example,a small monitoring camera may be mounted on a rearview mirror of thevehicle to image moving vehicles, pedestrians, and other objects infront of the vehicle. Such a small monitoring camera may not simplyimage objects in front of and behind the vehicle, but may also be usedas a sensor to recognize the objects in front of and behind the vehicle.

In this regard, a monitoring camera used as a sensor requires a highresolution to be able to sense fine movements. The resolution of amonitoring camera used as a sensor can be increased using a brightoptical system. However, an excessively bright optical system can causethe internal temperature of a monitoring camera to increase, therebydecreasing the resolution thereof.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an optical imaging system may include a firstlens having refractive power; a second lens having refractive power; athird lens having refractive power and cemented to the second lens; afourth lens having refractive power; a fifth lens having refractivepower and cemented to the fourth lens; a sixth lens having refractivepower; a seventh lens having refractive power; and an eighth lens havingrefractive power; and the first to eighth lenses are sequentiallydisposed in numerical order beginning with the first lens from an objectside of the optical imaging system toward an imaging plane of theoptical imaging system.

The first lens may have negative refractive power.

The second lens may have negative refractive power.

The third lens may have positive refractive power.

The fourth lens may have positive refractive power.

The fifth lens may have negative refractive power.

The sixth lens may have positive refractive power.

The seventh lens may have negative refractive power.

The eighth lens may have positive refractive power.

The optical imaging system may further include a stop disposed betweentwo of the lenses; an overall refractive power of ones of the lensesdisposed between the object side of the optical imaging system and thestop may be negative; and an overall refractive power of ones of thelenses disposed between the stop and the imaging plane of the opticalimaging system may be positive.

The optical imaging system may satisfy the Conditional Expressionsf2<f1<0, f1<f5<0, f7<f5<0, 0<f4<f3, 0<f4<f6, and 0<f4<f8, where f1 is afocal length of the first lens, f2 is a focal length of the second lens,f3 is a focal length of the third lens, f4 is a focal length of thefourth lens, f5 is a focal length of the fifth lens, f6 is a focallength of the sixth lens, f7 is a focal length of the seventh lens, andf8 is a focal length of the eighth lens.

In another general aspect, an optical imaging system includes a firstlens, a second lens, a third lens, a stop, a fourth lens, a fifth lens,a sixth lens, a seventh lens, and an eighth lens sequentially disposedin numerical order beginning with the first lens from an object side ofthe optical imaging system toward an imaging plane of the opticalimaging system.

The first to third lenses and the eighth lens each may include a convexobject-side surface and a concave image-side surface.

The fourth lens may include a concave object-side surface and a conveximage-side surface.

The fifth lens may include a concave object-side surface and a conveximage-side surface; and the seventh lens may include a convexobject-image side surface and a concave image-side surface.

The sixth lens may include a convex object-image side surface and aconvex image-side surface.

The first lens and the second lens may have negative refractive power.

The third lens and the fourth lens may have positive refractive power.

The optical imaging system may further include a stop disposed betweentwo of the lenses; an overall refractive power of ones of the lensesdisposed between the object side of the optical imaging system and thestop may be negative; and an overall refractive power of ones of thelenses disposed between the stop and the imaging plane of the opticalimaging system may be positive.

The optical imaging system may satisfy the Conditional Expressionsf2<f1<0, f1<f5<0, f7<f5<0, 0<f4<f3, 0<f4<f6, 0<f4<f8, where f1 is afocal length of the first lens, f2 is a focal length of the second lens,f3 is a focal length of the third lens, f4 is a focal length of thefourth lens, f5 is a focal length of the fifth lens, f6 is a focallength of the sixth lens, f7 is a focal length of the seventh lens, andf8 is a focal length of the eighth lens.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view of an example of an optical imaging system.

FIG. 2 is a table listing an example of characteristics of lenses of theoptical imaging system illustrated in FIG. 1.

FIG. 3 is a graph illustrating an example of modulation transferfunction (MTF) characteristics of the optical imaging system illustratedin FIG. 1.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art may be omitted forincreased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

In this application, a first lens is a lens closest to an object or asubject, while an eighth lens is a lens closest to an imaging plane oran image sensor.

In this application, radii of curvature, thicknesses, total tracklengths (TTLs), and focal lengths of lenses are expressed in millimeters(mm). Further, the thicknesses of the lenses, gaps between the lenses,and the TTLs are distances measured along the optical axes of thelenses.

Further, concerning shapes of the lenses, such shapes are described inrelation to the optical axes of the lenses. A surface of a lensdescribed as convex means that an optical axis portion of acorresponding surface is convex, and a surface of a lens described asconcave means that an optical axis portion of a corresponding surface isconcave. Therefore, in a configuration in which one surface of a lens isdescribed as being convex, an edge portion of that surface of the lensmay be concave. Likewise, in a configuration in which one surface of alens is described as being concave, an edge portion of that surface ofthe lens may be convex.

An optical imaging system includes a plurality of lenses. For example,the optical imaging system may include eight lenses. Next,configurations of the lenses described above are described.

The first lens has refractive power. For example, the first lens mayhave negative refractive power.

One surface of the first lens is convex. For example, an object-sidesurface of the first lens may be convex.

The first lens has a spherical surface. For example, both surfaces ofthe first lens may be spherical. The first lens is formed of a materialhaving high light transmissivity and excellent workability. For example,the first lens may be formed of glass. However, a material of the firstlens is not limited thereto. For example, the first lens may be formedof plastic.

The first lens has a certain refractive index. For example, a refractiveindex of the first lens may be 1.70 or less. The first lens has an Abbenumber lower than that of the second lens. For example, the Abbe numberof the first lens may be 60 or less.

The second lens has refractive power. For example, the second lens mayhave negative refractive power.

One surface of the second lens is convex. For example, an object-sidesurface of the second lens may be convex.

The second lens includes a spherical surface. For example, both surfacesof the second lens may be spherical. The second lens is formed of amaterial having high light transmissivity and excellent workability. Forexample, the second lens may be formed of glass. However, a material ofthe second lens is not limited thereto. For example, the second lens maybe formed of plastic.

The second lens has a certain refractive index. For example, arefractive index of the second lens may be 1.70 or more. The second lensmay have an Abbe number higher than those of other lenses. For example,the Abbe number of the second lens may be 80 or more.

The third lens has refractive power. For example, the third lens mayhave positive refractive power.

One surface of the third lens is convex. For example, an object-sidesurface of the third lens may be convex.

The third lens includes a spherical surface. For example, both surfacesof the third lens may be spherical. The third lens is formed of amaterial having high light transmissivity and excellent workability. Forexample, the third lens may be formed of glass. However, a material ofthe third lens is not limited thereto. For example, the third lens maybe formed of plastic.

The third lens has a certain refractive index. For example, a refractiveindex of the third lens may be 1.90 or more. The third lens has an Abbenumber lower than those of other lenses. For example, the Abbe number ofthe third lens may be 25 or less.

The fourth lens has refractive power. For example, the fourth lens mayhave positive refractive power.

One surface of the fourth lens is concave. For example, an object-sidesurface of the fourth lens may be concave.

The fourth lens includes a spherical surface. For example, both surfacesof the fourth lens may be spherical. The fourth lens is formed of amaterial having high light transmissivity and excellent workability. Forexample, the fourth lens may be formed of glass. However, a material ofthe fourth lens is not limited thereto. For example, the fourth lens maybe formed of plastic.

The fourth lens has a certain refractive index. For example, arefractive index of the first lens may be 1.80 or less. The fourth lensmay have an Abbe number higher than those of lenses adjacent thereto,that is, the third lens and the fifth lens. For example, the Abbe numberof the fourth lens may be 50 or more.

The fifth lens has refractive power. For example, the fifth lens mayhave negative refractive power.

One surface of the fifth lens is concave. For example, an object-sidesurface of the fifth lens may be concave.

The fifth lens includes a spherical surface. For example, both surfacesof the fifth lens may be spherical. The fifth lens may be formed of amaterial having high light transmissivity and excellent workability. Forexample, the fifth lens may be formed of glass. However, a material ofthe fifth lens is not limited thereto. For example, the fifth lens maybe formed of plastic.

The fifth lens has a certain refractive index. For example, a refractiveindex of the fifth lens may be 1.90 or more. The fifth lens has an Abbenumber lower than those of lenses adjacent thereto, that is, the fourthlens and the sixth lens. For example, the Abbe number of the fifth lensmay be 20 or less.

The sixth lens has refractive power. For example, the sixth lens mayhave positive refractive power.

One surface of the sixth lens is convex. For example, an object-sidesurface of the sixth lens may be convex.

The sixth lens includes a spherical surface. For example, both surfacesof the sixth lens may be spherical. The sixth lens is formed of amaterial having high light transmissivity and excellent workability. Forexample, the sixth lens may be formed of glass. However, a material ofthe sixth lens is not limited thereto. For example, the sixth lens maybe formed of plastic.

The sixth lens has a certain refractive index. For example, a refractiveindex of the sixth lens may be 1.80 or less. The sixth lens has an Abbenumber higher than those of lenses adjacent thereto, that is, the fifthlens and the seventh lens. For example, the Abbe number of the sixthlens may be 50 or more.

The seventh lens has refractive power. For example, the seventh lens mayhave negative refractive power.

One surface of the seventh lens is convex. For example, an object-sidesurface of the seventh lens may be convex.

The seventh lens includes a spherical surface. For example, bothsurfaces of the seventh lens may be spherical. The seventh lens isformed of a material having high light transmissivity and excellentworkability. For example, the seventh lens may be formed of glass.However, a material of the seventh lens is not limited thereto. Forexample, the seventh lens may be formed of plastic.

The seventh lens has a certain refractive index. For example, arefractive index of the seventh lens may be 1.90 or more. The seventhlens has an Abbe number lower than those of lenses adjacent thereto,that is, the sixth lens and the eighth lens. For example, the Abbenumber of the seventh lens may be 30 or less.

The eighth lens has refractive power. For example, the eighth lens mayhave positive refractive power.

One surface of the eighth lens is convex. For example, an object-sidesurface of the eighth lens may be convex.

The eighth lens includes a spherical surface. For example, both surfacesof the eighth lens may be spherical. The eighth lens is formed of amaterial having high light transmissivity and excellent workability. Forexample, the eighth lens may be formed of glass. However, a material ofthe eighth lens is not limited thereto. For example, the eighth lens maybe formed of plastic.

The eighth lens has a certain refractive index. For example, arefractive index of the eighth lens may be 1.80 or less. The eighth lenshas an Abbe number higher than that of the seventh lens. For example,the Abbe number of the eighth lens may be 50 or more.

The optical imaging system includes an image sensor. The image sensor isconfigured to have a high resolution. For example, a unit size of pixelsforming the image sensor may be 1.12 μm or less. A surface of the imagesensor forms an imaging plane on which an image is formed.

The optical imaging system includes a stop. The stop is disposed betweentwo of the lenses of the optical imaging system. For example, the stopmay be disposed between the third and fourth lenses. The stop disposedin this location adjusts an amount of light incident to the imagesensor.

The stop is disposed to bisect the refractive power of the opticalimaging system. For example, the overall refractive power of the lensesof the optical imaging system positioned in front of the stop (that is,positioned adjacent to the object) may be negative, and the overallrefractive power of the lenses of the optical imaging system positionedbehind the stop (that is, positioned adjacent to the imaging plane) maybe positive. This structure is advantageous in increasing a field ofview of the optical imaging system and decreasing an overall length ofthe optical imaging system.

The optical imaging system includes a filter. The filter is disposedbetween the eighth lens and the image sensor to filter componentsdecreasing resolution. For example, the filter may filter light havingan infrared wavelength. The filter has a certain refractive index. Forexample, a refractive index of the filter may be 1.50 or more. Thefilter has an Abbe number higher than that of the eighth lens. Forexample, the Abbe number of the filter may be 60 or more.

The optical imaging system satisfies the following ConditionalExpressions:

f2<f1<0

f1<f5<0

f7<f5<0

0<f4<f3

0<f4<f6

0<f4<f8

In the above Conditional Expressions, f1 is a focal length of the firstlens, f2 is a focal length of the second lens, f3 is a focal length ofthe third lens, f4 is a focal length of the fourth lens, f5 is a focallength of the fifth lens, f6 is a focal length of the sixth lens, f7 isa focal length of the seventh lens, and f8 is a focal length of theeighth lens.

The above Conditional Expressions are relationships for appropriatelydistributing refractive power to the first to eighth lenses. Forexample, all of the first lens, the second lens, the fifth lens, and theseventh lens may be configured to have negative refractive power.Further, all of the third lens, the fourth lens, the sixth lens, and theeighth lens may be configured to have positive refractive power.

The fifth lens has the strongest refractive power among the lenseshaving negative refractive power. The fourth lens has the strongestrefractive power among the lenses having positive refractive power.

The optical imaging system configured as described above has a highresolution. For example, the optical imaging system may have an F numberof 1.6 or less. Thus, the optical imaging system may be employed in asmall sensing camera. Further, the optical imaging system has a widefield of view. For example, the optical imaging system may have ahorizontal field of view of 75° or higher. Thus, the optical imagingsystem may be employed in a monitoring camera which images a frontvisual field and a side visual field of a vehicle.

Next, an example of an optical imaging system is described.

FIG. 1 is a view of an example of an optical imaging system.

An optical imaging system 100 includes a plurality of lenses havingrefractive power. For example, the optical imaging system 100 includes afirst lens 110, a second lens 120, a third lens 130, a fourth lens 140,a fifth lens 150, a sixth lens 160, a seventh lens 170, and an eighthlens 180. The first lens 110 to the eighth lens 180 are disposed innumerical order beginning with the first lens 110 from an object side ofthe optical imaging system 100 toward an imaging plane 108 of theoptical imaging system.

In one example, the first lens 110 has negative refractive power, anobject-side surface thereof is convex, and an image-side surface thereofis concave. The second lens 120 has negative refractive power, anobject-side surface thereof is convex, and an image-side surface thereofis concave. The third lens 130 has positive refractive power, anobject-side surface thereof is convex, and an image-side surface thereofis concave. The fourth lens 140 has positive refractive power, anobject-side surface thereof is concave, and an image-side surfacethereof is convex. The fifth lens 150 has negative refractive power, anobject-side surface thereof is concave, and an image-side surfacethereof is convex. The sixth lens 160 has positive refractive power, andan object-side surface and an image-side surface thereof are convex. Theseventh lens 170 has negative refractive power, an object-side surfacethereof is convex, and an image-side surface thereof is concave. Theeighth lens 180 has positive refractive power, an object-side surfacethereof is convex, and an image-side surface thereof is concave.

In the configuration as described above, the sixth lens 160 and theseventh lens 170 are configured to reduce astigmatic aberration anddistortion aberration. In one example, the sixth lens 160 and theseventh lens 170 have a convex object-side surface formed thereon toreduce aberrations caused by the first to fifth lenses 110 to 150. Inanother example, the sixth lens 160 and the seventh lens 170 areconfigured to have substantially weak refractive power to reduceaberrations caused by the first to fifth lenses 110 to 150.

The optical imaging system 100 includes a stop ST. The stop ST isdisposed between the third lens 130 and the fourth lens 140. The stop STdisposed in this location may increase a resolution of the opticalimaging system 100 by blocking ambient light that causes lateralaberration (coma), astigmatism, rectilinear distortion, or lateralchromatic aberration.

The optical imaging system 100 includes a filter 190. The filter 190 isdisposed between the eighth lens 180 and the imaging plane 108. Thefilter 190 may block infrared light, and may prevent foreign substancesfrom being introduced from the imaging plane 108.

The optical imaging system 100 includes an image sensor. The imagesensor includes the imaging plane 108 on which light refracted by thefirst to eighth lenses 110 to 180 is focused.

The optical imaging system 100 includes a plurality of cemented lenses.For example, the optical imaging system 100 includes a pair of a firstcemented lens CL1 formed by cementing the second lens 120 to the thirdlens 130, and a second cemented lens CL2 formed by cementing the fourthlens 140 to the fifth lens 150.

The first and second cemented lenses CL1 and CL2 are symmetrical to eachother around the stop ST. For example, all of the first and secondcemented lenses CL1 and CL2 may have positive refractive power. Further,the first cemented lens CL1 is convex toward the object, and the secondcemented lens CL2 is convex toward the imaging plane.

The pair of first and second cemented lenses CL1 and CL2 configured asdescribed above may compensate for Seidel aberration, rectilineardistortion, coma, or lateral chromatic aberration preventing formationof a clear image.

The second cemented lens CL2 is symmetrical to the seventh lens 170 andthe eighth lens 180. In one example, the fourth lens 140 of the secondcemented lens CL2 is symmetrical to the eighth lens 180, and the fifthlens 150 of the second cemented lens CL2 is symmetrical to the seventhlens 170. In another example, the fourth lens 140 of the second cementedlens CL2 has the same refractive power as the eighth lens 180, and thefifth lens 150 of the second cemented lens CL2 has the same refractivepower as the seventh lens 170.

FIG. 2 is a table listing an example of characteristics of the lenses ofthe optical imaging system 100 illustrated in FIG. 1.

All of the first to eighth lenses 110 to 180 are formed of glass. Theoptical imaging system 100 configured as described above may realize asharp, clear image.

The third lens 130, the fifth lens 150, and the seventh lens 170 areformed of a high refractive material. For example, all of the third lens130, the fifth lens 150, and the seventh lens 170 have a refractiveindex of 1.90 or more.

The third lens 130, the fifth lens 150, and the seventh lens 170 areconfigured to reduce chromatic aberration caused by lenses adjacentthereto. For example, all of the third lens 130, the fifth lens 150, andthe seventh lens 170 have an Abbe number lower than those of lensesadjacent thereto.

The second lens 120 is cemented to the third lens 130. For example, animage-side surface S4 of the second lens 120 is entirely adhered to anobject-side surface S5 of the third lens 130. To this end, a radius ofcurvature of the image-side surface S4 of the second lens 120 and aradius of curvature of the object-side surface S5 of the third lens 130are the same as each other.

The fourth lens 140 is cemented to the fifth lens 150. For example, animage-side surface S9 of the fourth lens 140 is entirely adhered to anobject-side surface S10 of the fifth lens 150. To this end, a radius ofcurvature of the image-side surface S9 of the fourth lens 140 and aradius of curvature of the object-side surface S10 of the fifth lens 150are the same as each other.

All of the first lens 110, the second lens 120, the fifth lens 150, andthe seventh lens 170 have a negative focal length. For example, all ofthe first lens 110, the second lens 120, the fifth lens 150, and theseventh lens 170 have negative refractive power. The fifth lens 150 hasthe maximum refractive power among the first lens 110, the second lens120, the fifth lens 150, and the seventh lens 170 having negativerefractive power.

All of the third lens 130, the fourth lens 140, the sixth lens 160, andthe eighth lens 180 have a positive focal length. For example, all ofthe third lens 130, the fourth lens 140, the sixth lens 160, and theeighth lens 180 have positive refractive power. The fourth lens 140 hasthe maximum refractive power among the third lens 130, the fourth lens140, the sixth lens 160, and the eighth lens 180 having positiverefractive power.

FIG. 3 is a graph illustrating an example of modulation transferfunction (MTF) characteristics of the optical imaging system 100illustrated in FIG. 1.

According to the examples of an optical imaging system described above,a high level of resolution may be realized even in a high temperatureenvironment.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system comprising: a firstlens having refractive power; a second lens having refractive power; athird lens having refractive power and cemented to the second lens; afourth lens having refractive power; a fifth lens having refractivepower and cemented to the fourth lens; a sixth lens having refractivepower; a seventh lens having refractive power; and an eighth lens havingrefractive power; wherein the first to eighth lenses are sequentiallydisposed in numerical order beginning with the first lens from an objectside of the optical imaging system toward an imaging plane of theoptical imaging system, the fifth lens has negative refractive power,and the seventh lens has negative refractive power.
 2. The opticalimaging system of claim 1, wherein the first lens has negativerefractive power.
 3. The optical imaging system of claim 1, wherein thesecond lens has negative refractive power.
 4. The optical imaging systemof claim 1, wherein the third lens has positive refractive power.
 5. Theoptical imaging system of claim 1, wherein the fourth lens has positiverefractive power.
 6. The optical imaging system of claim 1, wherein thesixth lens has positive refractive power.
 7. The optical imaging systemof claim 1, wherein the eighth lens has positive refractive power. 8.The optical imaging system of claim 1, further comprising a stopdisposed between two of the lenses; wherein an overall refractive powerof ones of the lenses disposed between the object side of the opticalimaging system and the stop is negative; and an overall refractive powerof ones of the lenses disposed between the stop and the imaging plane ofthe optical imaging system is positive.
 9. The optical imaging system ofclaim 1, wherein the optical imaging system satisfies the followingConditional Expressions: f2<f1<0 f1<f5<0 f7<f5<0 0<f4<f3 0<f4<f6 0<f4<f8where f1 is a focal length of the first lens, f2 is a focal length ofthe second lens, f3 is a focal length of the third lens, f4 is a focallength of the fourth lens, f5 is a focal length of the fifth lens, f6 isa focal length of the sixth lens, f7 is a focal length of the seventhlens, and f8 is a focal length of the eighth lens.